/*=========================================================================
 *
 *  Copyright UMC Utrecht and contributors
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
/*=========================================================================

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkBSplineDerivativeKernelFunction2.h,v $
  Language:  C++
  Date:      $Date: 2008-06-25 11:00:19 $
  Version:   $Revision: 1.7 $

  Copyright (c) Insight Software Consortium. All rights reserved.
  See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notices for more information.

=========================================================================*/
#ifndef __itkBSplineDerivativeKernelFunction2_h
#define __itkBSplineDerivativeKernelFunction2_h

#include "itkKernelFunctionBase2.h"
#include "vnl/vnl_math.h"

namespace itk
{

/** \class BSplineDerivativeKernelFunction2
 * \brief Derivative of a B-spline kernel used for density estimation and
 *  nonparametric regression.
 *
 * This class encapsulates the derivative of a B-spline kernel for
 * density estimation or nonparametric regression.
 * See documentation for KernelFunction for more details.
 *
 * This class is templated over the spline order.
 * \warning Evaluate is only implemented for spline order 1 to 4
 *
 * \sa KernelFunction
 *
 * \ingroup Functions
 */
template< unsigned int VSplineOrder = 3 >
class ITK_EXPORT BSplineDerivativeKernelFunction2 : public KernelFunctionBase2< double >
{
public:

  /** Standard class typedefs. */
  typedef BSplineDerivativeKernelFunction2 Self;
  typedef KernelFunctionBase2< double >    Superclass;
  typedef SmartPointer< Self >             Pointer;

  /** Method for creation through the object factory. */
  itkNewMacro( Self );

  /** Run-time type information (and related methods). */
  itkTypeMacro( BSplineDerivativeKernelFunction2, KernelFunctionBase2 );

  /** Enum of for spline order. */
  itkStaticConstMacro( SplineOrder, unsigned int, VSplineOrder );

  /** Evaluate the function. */
  inline double Evaluate( const double & u ) const override
  {
    return this->Evaluate( Dispatch< VSplineOrder >(), u );
  }


  /** Evaluate the function. */
  inline void Evaluate( const double & u, double * weights ) const override
  {
    return this->Evaluate( Dispatch< VSplineOrder >(), u, weights );
  }


protected:

  BSplineDerivativeKernelFunction2(){}
  ~BSplineDerivativeKernelFunction2() override{}

  void PrintSelf( std::ostream & os, Indent indent ) const override
  {
    Superclass::PrintSelf( os, indent );
    os << indent  << "Spline Order: " << SplineOrder << std::endl;
  }


private:

  BSplineDerivativeKernelFunction2( const Self & ); // purposely not implemented
  void operator=( const Self & );                   // purposely not implemented

  /** Structures to control overloaded versions of Evaluate */
  struct DispatchBase {};
  template< unsigned int >
  struct Dispatch : DispatchBase {};

  /** Zeroth order spline. */
  // Derivative not defined.

  /** First order spline */
  inline double Evaluate( const Dispatch< 1 > &, const double & u ) const
  {
    const double absValue = std::abs( u );

    if( absValue < NumericTraits< double >::OneValue() )
    {
      return -vnl_math::sgn( u );
    }
    else if( absValue == NumericTraits< double >::OneValue() )
    {
      return -vnl_math::sgn( u ) / 2.0;
    }
    else { return NumericTraits< double >::ZeroValue(); }
  }


  inline void Evaluate( const Dispatch< 1 > &, const double & u, double * weights ) const
  {
    // MS \todo: check
    const double absValue = std::abs( u );

    if( absValue < 1.0 && absValue > 0.0 )
    {
      weights[ 0 ] = -1.0;
      weights[ 1 ] = 1.0;
    }
    else if( absValue == 1 )
    {
      weights[ 0 ] = -0.5;
      weights[ 1 ] = 0.0;
    }
    else
    {
      weights[ 0 ] = 0.0;
      weights[ 1 ] = 0.5;
    }

  }


  /** Second order spline. */
  inline double Evaluate( const Dispatch< 2 > &, const double & u ) const
  {
    double absValue = std::abs( u );

    if( absValue < 0.5 )
    {
      return -2.0 * u;
    }
    else if( absValue < 1.5 )
    {
      return u - 1.5 * vnl_math::sgn( u );
    }
    else
    {
      return NumericTraits< double >::ZeroValue();
    }
  }


  inline void Evaluate( const Dispatch< 2 > &, const double & u, double * weights ) const
  {
    // MS \todo: check
    weights[ 0 ] =        u - 1.5;
    weights[ 1 ] = -2.0 * u + 2.0;
    weights[ 2 ] =        u - 0.5;
  }


  /**  Third order spline. */
  inline double Evaluate( const Dispatch< 3 > &, const double & u ) const
  {
    const double absValue = std::abs( u );
    const double sqrValue = u * u;

    if( absValue < 1.0 )
    {
      if( u > 0.0 )
      {
        const double dummy = std::abs( u + 0.5 );
        return ( 6.0 * sqrValue - 2.0 * u - 6.0 * dummy + 3.0 ) / 4.0;
      }
      else
      {
        const double dummy = std::abs( u - 0.5 );
        return -( 6.0 * sqrValue + 2.0 * u - 6.0 * dummy + 3.0 ) / 4.0;
      }
    }
    else if( absValue < 2.0 )
    {
      if( u > 0.0 )
      {
        const double dummy = std::abs( u - 0.5 );
        return ( u - sqrValue + 3.0 * dummy - 2.5 ) / 2.0;
      }
      else
      {
        const double dummy = std::abs( u + 0.5 );
        return ( u + sqrValue - 3.0 * dummy + 2.5 ) / 2.0;
      }
    }
    else
    {
      return 0.0;
    }
  }


  inline void Evaluate( const Dispatch< 3 > &, const double & u, double * weights ) const
  {
    const double absValue = std::abs( u );
    const double sqrValue = u * u;

    weights[ 0 ] =  0.5 * sqrValue - 2.0 * absValue + 2.0;
    weights[ 1 ] = -1.5 * sqrValue + 5.0 * absValue - 3.5;
    weights[ 2 ] =  1.5 * sqrValue - 4.0 * absValue + 2.0;
    weights[ 3 ] = -0.5 * sqrValue +       absValue - 0.5;
  }


  /** Unimplemented spline order */
  inline double Evaluate( const DispatchBase &, const double & ) const
  {
    itkExceptionMacro( "Evaluate not implemented for spline order " << SplineOrder );
    return 0.0; // This is to avoid compiler warning about missing
    // return statement.  It should never be evaluated.
  }


  /** Unimplemented spline order */
  inline void Evaluate( const DispatchBase &, const double &, double * ) const
  {
    itkExceptionMacro( "Evaluate not implemented for spline order " << SplineOrder );
  }


};

} // end namespace itk

#endif
